ZOOLOGY AN1> BOTANY, MICROSCOPY, ETC. 83 
the upper half of which is recessed a V-way with a T cross-cut, to which 
the arm is fitted. This combines extreme rigidity with compactness. 
Fig. 9. 
Recessed into the lower end of the pillar is a spring which forces the 
arm upward against a micrometer-screw which is attached to the upper 
G 2 
